Orthogonal frequency division multiplexing (OFDM) can be implemented by a simple equalizer and is robust against multipath fading. Thus, OFDM is employed for many wireless data communication systems such as a wireless local area network (WLAN), a wireless metropolitan area network (WMAN), digital audio broadcasting (DAB), digital video broadcasting (DVB), and the like.
However, OFDM has a high peak-to-average power ratio (PAPR) of up to 12 dB by the sum of signals having the same phase because it uses multiple carriers. Also, the operating point of a power amplifier of an OFDM transmitter is located in a nonlinear region due to high PAPR, and this results in nonlinear distortion of the signals. Hence, the OFDM system backs off the power amplifier in order to reduce the effects of the PAPR. Unless the power amplifier is sufficiently backed off, the frequency spectrum of the system is widened, and cross-frequency modulation causes distortion, resulting in degradation of system performance. Therefore, it is necessary to reduce the PARR to achieve the power efficiency of the OFDM transmitter and miniaturize the OFDM transmitter.
The use of a combination of the OFDM scheme having a high PAPR of up to 12 dB with a phase modulation (PM) scheme or frequency modulation (FM) scheme can reduce the PAPR to 0 dB.
A combination of the OFDM scheme and an analog PM or FM scheme causes degradation in reception performance in a channel with multiple paths, and the FM scheme requires a broad frequency band and shows more significant degradation in reception performance than the PM scheme.
While visible light communication (VLC) using OFDM becomes efficient when PAPR is reduced to 0 dB, light communication using light (e.g., infrared light) other than illumination requires a high PAPR to improve reception performance. Accordingly, undifferentiated PAPR control causes degradation in system performance.